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3.00 3.10
WINDOWS
kbprg
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) for Windows
versions 3.1 and 3.0
SUMMARY
An application can use the DrawIcon function in its paint procedure to
display a different icon for each application instance. The method
(outlined below) has five steps.
MORE INFORMATION
- In the WNDCLASS data structure used to register the application's
main window class, set the hIcon field to NULL. This prevents
Windows from drawing an icon when the application is minimized. The
following code demonstrates this step:
int index; // global variable to count application instances
// This function initializes the first application instance
void InitFirst(HANDLE hInstance)
{
WNDCLASS rClass; // window class structure
rClass.lpszClassName = "HELLO";
rClass.hInstance = hInstance;
rClass.lpfnWndProc = WindowProc;
rClass.hCursor = LoadCursor(NULL, IDC_ARROW);
// If hIcon is NULL, Windows will not draw icon. Application
// paints its own icon as appropriate.
rClass.hIcon = NULL;
rClass.lpszMenuName = NULL;
rClass.hbrBackground = COLOR_WINDOW + 1;
rClass.style = CS_HREDRAW | CS_VREDRAW;
rClass.cbClsExtra = 0;
rClass.cbWndExtra = 0;
RegisterClass(&rClass); // register the class
index = 1; // set counter to indicate first instance
}
- The GetInstanceData function provides the value of the instance
counter from the previous instance. Adding one to this value
provides the value for the current instance, as follows:
void InitNext(HANDLE hInstance, HANDLE hPrevInstance)
{
GetInstanceData(hPrevInstance, (PSTR)&index, sizeof(int));
index++;
}
- During the instance initialization function, load the icon for the
current instance from the application's resources. In this case,
Icon1, Icon2, Icon3, and Icon4 are individual icons declared in the
application's resources. The following code demonstrates this
procedure:
HICON hIcon; // icon handle for this instance
void InitEvery(HANDLE hInstance, int cmdShow)
{
HWND hWnd;
hInst = hInstance; // store instance in global variable for
// window procedures to use
switch (index)
{
case 1: hIcon = LoadIcon(hInstance, "Icon1");
break;
case 2: hIcon = LoadIcon(hInstance, "Icon2");
break;
case 3: hIcon = LoadIcon(hInstance, "Icon3");
break;
default:
hIcon = LoadIcon(hInstance, "Icon4");
}
CreateWindow( ... ); // and so forth
}
- When an application receives a WM_PAINT message while the window
is minimized, draw the icon in the application's client area. The
IsIconic function returns TRUE if the application is minimized.
The following code demonstrates this step:
// In the switch(message) statement of the main window procedure
case WM_PAINT:
{
PAINTSTRUCT ps;
if (IsIconic(hWnd))
{
BeginPaint(hWnd, (LPPAINTSTRUCT)&ps);
// Paint the desktop window background.
DefWindowProc(hWnd, WM_ICONERASEBKGND, (WORD)ps.hdc, 0L);
// Draw the icon in the cleared area
DrawIcon(ps.hdc, 0, 0, hIcon);
EndPaint(hWnd, (LPPAINTSTRUCT)&ps);
}
else
// Paint the window as usual
}
- When the user drags an application's icon with the mouse and the
application processes the WM_QUERYDRAGICON message as follows,
Windows changes the mouse cursor to a black-and-white
representation of the application's icon.
// In the switch(message) statement of the main window procedure
case WM_QUERYDRAGICON:
return (LONG)(WORD)hIcon;
break;
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